Scientists are beginning to trace the deep genetic roots that keep children like Alex locked in boxes of their brains’ own making. Researchers are linking rare changes in common brain chemicals and networks of genes with some of the symptoms that plague children with autism and their families. Scientists at Washington University and the University of Missouri are learning that people with autism are simply at one end of a continuum that encompasses us all.

A couple of other key quotes:

What is known is that autism is a genetic disorder. The identical twin of a child with autism has about a 65 percent chance of having autism and about a 90 percent chance of having one of the autism spectrum disorders, including Aspberger’s syndrome and PDD-NOS, said Dr. Eric Hollander, director of the Seaver Autism Center at Mount Sinai School of Medicine in New York. And siblings of autistic children, especially male siblings (boys are four times more likely than girls to have autism), have a higher risk of autism.

Some children get autism because their genes guide their brains to develop in a nontypical way. Miles calls the genetically based disorder “essential autism.” But environmental insults, such as toxins, and developmental missteps caused by hormone surges or other factors may also push a child into autism, Miles says. She calls this type of disorder “complex autism.”

Autism is not a “you have it or you don’t” disorder, Todd said. Instead, it is a highly inheritable continuum of traits, much like height or high blood pressure. The cutoff for being tall or short or having high or low blood pressure is somewhat arbitrary, he said. So is the diagnosis of autism. The measure of autism is usually the inability to cope in the real world, said NYU’s Hollander.

“People can be different without having a pathology,” Hollander said. “It’s only a disorder if it causes stress or interferes with function.”